Neural stem cells (NSCs) of the central nervous system (CNS) have recently aroused a great deal of interest not only because of their importance in basic research of neural development but also for their therapeutic potential for neurological diseases. Previously we have produced immortalized cell lines of human NSCs (Flax, et al. Nat Biotech. 1998;16:1033). Recently we have produced several more clones of human NSC lines via retrovirus-mediated v-myc transfer into embryonic human telencephalon cells. One of the NSC lines, HB 1/C4, is maintained as a stable cell line and remains uncommitted, undifferentiated, multipotent, and express nestin and vimentin, which are phenotypes specific for NSCs. Immortalized human NSCs have clinical utility for cell replacement and gene therapy for patients suffering from degenerative, developmental, and acquired neurological diseases. The HB 1/C4 cells carrying β-gal gene were stereotaxically implanted into brains of parkinsonian model rats and of myelin-mutant shiverer mice. Two to 6 weeks postoperation, implanted human NSCs were found to migrate extensively, integrate into host brain, and develop into neurons and/or glial cells as shown by immunohistochemistry. These results indicate that human NSCs are capable of survival, migration, and differentiation in animal models of Parkinson disease and multiple sclerosis. (Supported by the Canadian Myelin Research Initiative, Mississauga, Ontario, and Korea Social Engineering Foundation, South Korea.)